The thing with shipping for me, is that I have to really love both characters to want them to be together. Individually they have to be wonderful as well as together.
I can't get onboard the whole Jack/Avery (I hated typing that:embarrassment

thing, because I don't believe in them as a couple. I really don't like Avery as a character. She doesn't have the warmth and adorable character of Liz. I find her too aggressive and cold.
I've watched the Jack/Liz relationship develop throughout the seasons, seen it change and seen them become good friends. It's 'real' in the way that it has developed and it feels it. I just wish the writers would be brave and develop it further. The show would still be laugh out loud funny, but have heart and a solid core, which it seems to have lost lately.
I find it hard to accept that a man can be in love with two women at once, that doesn't fly with me I'm afraid. I believe that if Jack truely loved either woman, he wouldn't have been fooling around behind the others back.
The whole relationship just feels too forced for me. I've seen it before on programmes where writers force the chemistry between the characters and put them in a relationship. It doesn't work. This is what I feel the writers are doing to Jack/Avery. They don't have that chemistry, but because they don't want Jack/Liz in a relationship, it feels as though they are pushing the Jack/Avery relationship, especially by the pregnancy storyline.
Hope that makes sense.